Tighter emission standards and significant innovation in catalyst formulations and engine controls has led to dramatic improvements in the low emission performance and robustness of gasoline and diesel engine systems. However, many technical challenges remain to make the conventionally fueled internal combustion engine a nearly zero emission system having the efficiency necessary to make the vehicle commercially viable.
The automotive industry has made very significant progress in reducing automotive emissions in both the mandated test procedures and the “real world”. This has resulted in some added cost and complexity of engine management systems, yet those costs are offset by other advantages of computer controls: increased power density, fuel efficiency, drivability, reliability and real-time diagnostics. However future initiatives to require zero emission vehicles are likely to provide smaller environmental benefits at a very large incremental cost. Even so, an “ultra low emission” certified vehicle may emit high emissions in limited extreme ambient and operating conditions or with failed or degraded components, and especially during cold start.
One approach to addressing the issue of emissions is the employment of fuel cells, particularly solid oxide fuel cells (SOFC), in an automobile as either a primary or secondary source of power. A fuel cell is an energy conversion device that generates electricity and heat by electrochemically combining a gaseous fuel, such as hydrogen, carbon monoxide, or a hydrocarbon, and an oxidant, such as air or oxygen, across an ion-conducting electrolyte. The fuel cell converts chemical energy into electrical energy. SOFCs are constructed entirely of solid-state materials, utilizing an ion conductive oxide ceramic as the electrolyte. An electrochemical cell in a SOFC may comprise an anode and a cathode with an electrolyte disposed there between. The oxidant passes over the oxygen electrode (cathode) while the fuel passes over the fuel electrode (anode), generating electricity, water, and heat. The use of the SOFC, and fuel cells in general, reduce emissions through their much greater efficiency, and so require less fuel for the same amount of power produced, as compared to conventional hydrocarbon fueled engines. Additionally, a fuel cell may be employed to supplement a conventional engine; in this way the engine may be optimized for primary traction power, while the fuel cell may provide other power needs for the vehicle, i.e. air-conditioner, communication and entertainment devices. The fuel reformer-fuel cell system may be operated while the engine is off, permitting electrically powered devices to operate, thereby further reducing emissions by providing power using a more fuel efficient fuel cell to meet the vehicle operator's needs.
To facilitate the production of electricity by the SOFC, a direct supply of simple fuel, e.g., hydrogen, carbon monoxide, and/or methane is preferred. However, concentrated supplies of these fuels are generally expensive and difficult to supply. Therefore the fuel utilized may be obtained by processing a more complex fuel source. The actual fuel utilized in the system is chosen based upon the application, expense, availability, and environmental issues relating to the fuel. Possible fuels include hydrocarbon fuels, including, but not limited to, liquid fuels, such as gasoline, diesel fuel, ethanol, methanol, kerosene, and others; gaseous fuels, such as natural gas, propane, butane, and others; “alternative” fuels, such as biofuels, dimethyl ether, and others; synthetic fuels, such as synthetic fuels produced from methane, methanol, coal gasification or natural gas conversion to liquids, and combinations comprising at least one of the foregoing methods, and the like, as well as combinations comprising at least one of the foregoing fuels. The preferred fuel is based upon the types of equipment employed, with lighter fuels, i.e., those that may be more readily vaporized and/or conventional fuels, which are readily available to consumers being generally preferred.
Processing or reforming of hydrocarbon fuels such as gasoline may provide an immediate fuel source for rapid start up of the fuel cell and also protect the fuel cell by breaking down long chain hydrocarbons and removing impurities. Fuel reforming may include mixing fuel with air, water and/or steam in a reforming zone before entering the reformer system, and converting a hydrocarbon such as gasoline or an oxygenated fuel such as methanol into hydrogen (H2) and carbon monoxide (CO), along with carbon dioxide (CO2) methane (CH4), nitrogen (N2), and water (H2O). Approaches to reforming include steam reforming, partial oxidation, dry reforming, and combinations thereof. Both steam reforming and dry reforming are endothermic processes, while partial oxidation is an exothermic process.
Accordingly, a SOFC may be used in conjunction with a fuel reformer to convert a hydrocarbon-based fuel to hydrogen and carbon monoxide (the reformate) usable by a fuel cell. Preferably, the reformer has a rapid start, a dynamic response time, and excellent fuel conversion efficiency. It is also preferred for the reformer to have a minimal size and reduced weight, as compared to other power sources. However, reformers operate at temperatures that are typically higher than about 600° C., and may even exceed 1000° C. At lower temperatures, for example during start-up, deposition of carbonaceous matter, or soot, upon the catalyst may adversely affect the reformer's efficiency, reduce reformer life, and/or damage fuel cell components. Accordingly, it is beneficial to reduce the time required by a reformer and/or fuel cell system to reach an operational temperature.
Of the various types of reformers available, the type of reformer technologies preferred depend in part on the type of fuel to be used. Steam reformers (SR) are generally employed for converting methanol to hydrogen. Partial oxidation (PDX) reformers are generally employed for converting gasoline to hydrogen and carbon monoxide.
Steam reforming systems involve the use of a fuel and steam (H2O) that is reacted in heated tubes filled with catalysts to convert the hydrocarbons into principally hydrogen and carbon monoxide. The steam reforming reactions are endothermic; thus the steam reformer reactors are designed to transfer heat into the catalytic process. An example of the steam reforming reaction is as follows:CH4+H2O→CO+3H2 
Partial oxidation reformers are based on substoichiometric combustion to achieve the temperatures necessary to reform the hydrocarbon fuel. Decomposition of the fuel to primarily hydrogen and carbon monoxide occurs through thermal reactions at high temperatures of about 600° C. to about 1200° C., and preferably, about 700° C. to about 1050° C. Catalysts have been used with partial oxidation systems to promote conversion of various low sulfur fuels into synthesis gas. The use of a catalyst may result in acceleration of the reforming reactions and also enable the use of lower reaction temperatures than would otherwise be required in the absence of a catalyst. An example of the partial oxidation reforming reaction is as follows:CH4+½O2→CO+2H2 
U.S. Pat. No. 2,892,693, the disclosure of which is incorporated herein by reference, discloses a method for producing carbon monoxide and hydrogen from gaseous hydrocarbons in which steam is reacted with the hydrocarbon at an elevated pressure over a catalyst to effect partial conversion of the hydrocarbon, followed by reaction of the unconverted hydrocarbon contained in the effluent from the steam-hydrocarbon reforming reaction with oxygen in a zone of partial combustion.
Dry reforming involves the creation of hydrogen and carbon monoxide in the absence of water using, for example, carbon dioxide as the oxidant. Dry reforming reactions, like steam reforming reactions, are endothermic processes. An example of the dry reforming reaction is depicted in the following reaction:CH4+CO2→2CO+2H2 
Practical reformer systems may include a combination of these idealized processes. Thus, a combination of air, water and/or recycled engine exhaust gas may be used as the oxidant in the fuel reforming process.